Electric synchronizing apparatus



' March 29, 1932. T R. WARREN ELECTRIC SYNCHRONIZING APPARATUS FiledSept. 19, 1928 2 Sheets$heet l I March 29, 1932.

T. R. WARREN ELECTRIC SYNCHRONIZING APPARATUS Filed Sept. 19, 1928 2Sheets$heet 2 machine may act Patented Mar. 29, 1932 ENE El? F i N FFiiFE THOMAS REGINALD WARREN, OF NORTON-ON-TEES, ENGLAND, ASSIGNOB, TO A.

REYROLLE & COMPANY LIMITED, 05 'GBEAT BRITAIN IIEBB'URN-ON-TYNE,ENGLAND, A COMPANY OF ELECTRIC SYNCHRONIZING APPARATUS Application filedSeptember 19, 1925, Serial No.

This invention relates to electric synchronizingapparatus forcontrollingthe speed or frequency of an A.

ing inparallel.

The apparatus according to the invention comprisesia source of E. M. F.of standard frequency, means for raising or lowering the speed of themachine to be controlled, and

one or'more relays which are operated in accordance with the relationbetween the machinespeedor frequency and the standard frequency andactselectlvely to operate the speed-control ing means. Conveniently therelays are energized from the source of E. M. F. of standard frequencyand from a second source of E. M. F. derived fromthe electric systemsupplied from the machine, and act to vary the speed ofthemachinetobring the frequencies oftheltwo sources of .E. M. F. into agreement.

.lVhen the invention is applied tothe control of the frequency ofanelectric system supplied from a group of dynamo-electric ,machines,devices responsive to the load conditions in the system and acting toensure a proper distribution of the load to the machines are preferablyemployed to cooperate withthe frequency-responsive relays in the controlof the system frequency. Thus when the share of'theload takenby anindividual machine lies outside predetermined limits, the load-sharingdevice associated with that to prevent the speed of the machine j frombeing altered by'the actionof the frequency-responsive relays if suchalteration would tend to-malre the load talren bythe machine deviatefurtherfrom such limits.

The system of relays normally responsive to the relation between thestandard frequency andthe frequency of the system may also be utilized,when required to control the synchronizing and bringing into circuit ofan additional machine. This may be effected providing a change-overrelay which acts to change over the connections of the system machinesare in phase with station may have a system 306,994, and in GreatBritain October 5, 1927.

of relays fromthe source of E. M. F. of standard frequency to a thirdsource of E. -M. F. derived from the incoming machine, the relays stillremaining connected to the second source of E. M. E. which is derivedfrom the system.

The manner in which the frequency-responsive relaysare arranged mayvary, but preferably an arrangement is employed similar to thatdescribed in the specification accompanying the concurrent applicationfor Letters Patent of the United States of America Serial No.271825, nowPatent Number 1,808,124, granted to Warren and Cooke. In thisspecification the relay arrangement is employed for the purpose ofcontrolling the connectionof an incoming machine into circuit withrunning machines, and preferably comprises a synchronizing relay whichre ceives its maximum energizing current when the voltages of theincoming and running one another, and an auxiliary. synchronizing relaywhich acts to render the synchronizing relay inoperative for onedirection of relative-rotation of the incoming and running machines,these relays acting through other relays to control the speed of theincoming machine and its connection into circuit.

This arrangement may readily be extended to the remote frequencyand'load control on a number of substations over pilot wirestfrom a.control station. Thus in one convenientarrangement the source ofEllLF.ofstandard frcquenc rand the system of frequency con trolling-relays arelocated at the control station, whilst a source of EMF. derived from thesystem in each substation can be connected to the system ofrelaysthrough pilot wires. Each substation is provided with devices forautomatically sharing the load amongstthe individual machines in thesubstation, and hand-operated means are provided at the control stationfor controlling the distribution of load amongst the substations, oratedmeans or the frequency-controlling relays-acting in conjunction with theautomatic loadesharing devices-to control the speed-0f the machines ineach substation. Each subof relaysfor consuch hand-on trolling thesynchronizing and bringing into circuit of an additional machine, and aselective remote control arrangement may be provided whereby an operatorat the control station can select an individual machine and cause theselected machine to be synchronized and brought into circuit under thecontrol of such system of relays. V

' The invention may be carried into practice in various ways, but twoconvenient arrangements according thereto are illustrated by way ofexample in the accompanying drawings, in which Figure 1 shows theapplication of the invention to the control of an adjacent group ofmachines operating in parallel, and

Figure 2 illustrates the application of the invention to the remotecontrol of a number of substations.

In the arrangement of Figure 1 each machine A is provided with apotential transformer A whose secondary phase-windings A A A areconnected in star on one side. The free end of one secondaryphase-winding A is-earthed and those of the other windings A A areconnected to sockets into which synchronizing and busbar plugs can beinserted. Thus the lagging phase A of each secondary may be connectedthrough a busbar plug B to a lagging phase busbar C, and

.the leading phase A may be connected either through a synchronizingchronizing busbar or through a busbar plug B to a leading phase busbar CThe busbar plugs B B are inserted in their sockets plug B to a synwhenthe corresponding machines are in 0peration and connected tothe loadcircuit,

' whilst the synchronizing plugs B are only inserted when thecorresponding machine is to be synchronized and brought into circuit.These three busbars C C C lead to the synchronizing apparatus.

In order to control the frequency of the system supplied by themachines, a constant speed motor-generator set is provided, comprlslng aerator D one side of which is earthed whilst phase the other isconnected to the synchronizing apparatus now to bedescribed.

A resistance E having a mid-point tapping is connected on one side tothe leading busbar C and on the other side to two of the sets ofcontacts F F of a change-over relay F, these contacts being connected onthe other side respectively to the synchronizing busbar C and to thelead from the A. C. generator D The operating coil of the changeoverrelay Fis' connected between earth and busbar C and the relay istherefore only energized to connect the synchronizing busbar C to theresistance E when a synchronizing plug B is inserted.

The mid-point tapping on the resistance E? is connected to one side of asynchronizing relay E, the other side of which is connected D. C. motorD driving an A. C. gen-- to earth through normally open contacts G on anauxiliary synchronizing relay G. This auxiliary synchronizing relay isconnected on one side to the synchronizing busbar C or to the lead fromthe A. G. generator D and on the other side to a mid-point tapping on aresistance G connected between the leading and lagging phase busbars CC. Thus the synchronizing relay. E cannot lift its contacts unless theauxiliary synchronizing relay G has already been energized, but when itdoes so it at once makes its own retaining circuit at contacts E so thatthe fall of the contacts is independent of the ball of the auxiliarysynchronizing relay contacts G In addition to the two synchronizingrelays E G, the synchronizing apparatus includes also a time-lag relay Hand an interrupter relay J, which can be energized from a D. C. source C6*. The energizing circuit'for the time-lag relay H is taken through aresistance H and through normally open contacts E and G on thesynchronizing relay E and the auxiliary synchronizing relay G. Thus whenboth synchronizing relays E G are energized, the contacts of thetime-lag relay H begin to lift this relay completing its own retainingcircuit at contacts H to render it independent of the auxiliarysynchronizing relay Gr as soon as the lifting movement has commenced.This time-lag relay H however still remains dependent on thesynchronizing relay E and its contacts fall instantaneously as soon asthe synchronizing relay contacts E fall.

The interrupter relay J, which also has a time-lag associated with itslift but not its control busbars C 0 Thus when the synchronizing relay Eis deenergized this circuit leads to one speed-control busbar C whilstwhen the synchronizing relay contacts E are lifted the otherspeed-control busbar C is connected up. V I

Normally closed contacts G on the aux iliary synchronizing'relay G andnormally open contacts H on the time-lag relay H also control a circuitfrom the D. C. busbar C to a circuit-breaker closing busbar 0 j Thechange-over relay F besides controlling the circuits fromthesynchronizing busbar C and from the A. C. generator D has other sets ofcontacts, one of which F acts to short-circuit the time-lag relay H whenthe change-over relay F is deenergized, whilst two others F 3 1" (onenormally open and one normally closed) are connected in parallel in theearth connection from the synchronizing relay E, so that as soon as thechange-over rela F is operated the synchronizing relay is deenergized,the completion of the movement of the change-over relay contacts F afterits time-lag however reestablishing the energizing circuit for thesynchronizing relay E. The reason for this will be explained later.

The two speed-control busbars C C serve to carry energizing currentrespectively to a raise-speed contactor K and a lower-speed contactor Kwith which each machine A is provided. These contactors K K control thepolarity of the energizing current supplied from the D. C. busbars C Cto an auxiliary motor K which controls the speed of the machine A, forexample by operating the governing mechanism K of a steam turbine orother prime mover (indicated at K by which the machine A is driven. Thuswhen the raise-speed contactor K is ener ized the auxiliary motor K isdriven in one direction to raise the machine speed, whilst theenergization of the lower-speed contactor K causes the auxiliary motor Kto be driven in the reverse direction to lower the machine speed. Thecircuits from the two speed-control busbars C C to the two contactors KK are taken through auxiliary change-over contacts L L on the maincircuit-breaker L which connects the machine A to the load circuit, andthence according to whether the circuitbreaker L is open or closedeither through synchronizing auxiliary contacts B B which are closedwhen the machine is to be synchronized and connected to the load circuitor through interlock contacts M M on a load-sharing device M associatedwith the machine, each speed-control busbar thus being connectedalternatively to the raisespeed contactor K or to the lower-speedcontactor K in accordance with the position of the circuit-breaker. Thecircuit-breaker closing busbar G is connected to the closing coil L ofthe main circuit-breaker L of each machine through synchronizingauxiliary contacts B closed only when the machine is to be synchronized.Auxiliary contacts L on the circuit-breaker L control the energizingcircuit to the raise-speed and lower-speed cont-actors K K so that whenthe circuitbreaker is open these cont actors are directly connected tothe D. C. busbar C whilst when the circuit-breaker is closed thisconnection is taken through the contacts F 5 on the change-over relay.

Any suitable load-sharin arrangement may be used which is such as toensure a proper distribution of load among the running machines.Conveniently the load-sharing arrangement forming the subject of theco-pending application for Letters Patent of the United States ofAmerica Serial N 0.

274890 filed May 3, 1928, now Patent Number 1,714,656. When thisarrangement is applied to the present system, each machine A is providedwith a relay M of the wattmeter type, having a voltage coil M connectedbetween earth and the lagging phase A of the potential transformer A andtwo differentially arranged current coils M M The current coil M isconnected in series with the secondary A of a current transformerconnected to the machine terminals, and the current transformersecondaries A on all the machines are connected in parallel to summationbusbars C C through auxiliary contacts L on the circuit-breakers L,these contacts L being open when the circuit-breakers are open. Thus thecurrent coil M is energized in accordance with the load on theassociated machine, whilst the other current coil M which is connectedacross the summation busbars C C through auxiliary contacts L open whenthe circuit-breaker L is open, is energized in accordance with theaverage load on all the machines in commission. The interlock contacts MM on the relay M are so arranged that both are normally closed, but thatone of them M opens when the machine is taking too great a load and thusprevents the energization of the raise-speed contactor K, whilst theother M opens when the machine is taking too small a load to preventenergization of the lower-speed contactor K The operation of theapparatus will now be described first of all with reference to frequencycontrol for a number of running machines when the conditions are notsuch as to require bringing an additional machine into circuit. In thiscase all the synchronizing plugs B B B B will be out of their sockets sothat the synchronizing busbar C is deenergized whilst the busbar plugs BB associated with the running machines are in their sockets to energizethe leading and lagging phase busbars C C wing to the deenergization ofthe synchronizing busbar C the changeover relay F will he deenergizcd,with the result that the time-lag relay H is short-circuited whilst thesynchronizing and auxiliary synchronizing relays E G are connected up tocompare the frequency of the system supplied by the running machineswith that of the A. C. generator D So long as the two frequencies are inagreement the synchronizing relay contacts will be lifted and theauxiliary synchronizing relay G will be deenergized so that theinterrupter relay contacts J J are in their lifted position. Under theseconditions the two speed-control busbars C C (which are connected to thetwo speed-control contactors K K of each running machine through thecircuit-breaker auxiliary contacts L L and the wattmeter relay contactsM M are deenergized.

If now the load conditions in the load circuit change to anyconsiderable extent, the re- The manner of operation of the synchronizing relays can best be described with reference to the rotation ofthe needle of a rotary synchroscope, which will be assumed to beconnected up in the usual manner to indicate the relationship betweenthe two frequencies.

The synchronizing relay E receives its maximum energizing current whenthe synchronoscope needle reaches its synchronizing position, and is setto lift its contacts before that position is reached, these contactsfalling 150 after the synchronizing position is passed. The voltageacross the operating coil of the auxiliary synchronizing relay G becomeszero 30 after the synchronizingposition is reached when the frequency ofthe system is less than the frequency of the A. C. generator or 30before the synchronizing position if the system frequency is greaterthan that of the A. C. generator D This relay G is set to lift itscontacts 120 after its zero position is passed, the contacts falling 35before the zero position is reached. 7 Thus with the system frequencytoo high the auxiliary relay G will lift its contacts 90 after thesynchronizing position and will drop them again before the synchronizingposition, so that the contacts G will be down during the period when thesynchronizing relay E could be energized. The synchronizing relay Etherefore remains inoperative so long as the system frequency is toohigh. On the other hand with the system frequency too low the auxiliarysynchronizing relay G will lift its contacts 150 after the synchronizingposition and drop them 5 before the synchronizing position, whilst thesynchronizing relay contacts will lift 50 before the syn= chronizingposition and fall 150 after the synchronizing position simultaneouslywith the lifting of the auxiliary synchronizing relay contacts.

If new the change in load conditions has caused the system frequency tobe increased, the auxiliary synchronizing relay contactsG willrepeatedly rise and fall but the synchronizing relay E will remaindeenergized and will thus prepare the circuit through one speed-controlbusbar C and such wattmeter interlock contacts M as are closed to thelower-speed ccntactors K This circuit is controlled by normally closedcontacts G and J on the auxiliary synchronizing relay and on theinterrupter relay J. If the change in frequency has'been large thesynchroscope needle will be rotating too fast for the interrupter relayJ to operate its contacts, and

consequently the energizing current supplied to the lower-speedccntactors K and therefore also to the corresponding auxiliary motors Kwill be intermittentlyinterrupted owing to the rise and fall of theauxiliary synchronizing relay contacts G. Thus the speed of all themachines (except those taking too small a load) is lowered gradually andthe frequency of the system tends to approach the standard frequency. Ata predetermined point in the approach to equality of frequencies, thetime allowed for the lift ing of the interrupter relay contacts Jbecomes sufhcient for them to complete their lift before the lifting ofthe auxiliary synchronizing relay contacts G and from then onwards theamount of interruption in the supply of energizing currents totheauxiliary motors K is increased, so that the approach tosynchronismbecomes more gradual. Ultimately the state of synchronism isreestablished and the load-sharing devices M complete their operation ofuniformly distributing the load.

In the case when the load change acts to decrease the systemfrequencyboth synchro nizing relays E G repeatedly operate but in such a mannerthat the auxiliary synchronizing relay contacts G are never downwhen thesynchronizing relay contacts E are down. Thus current is intermittentlysupplied to the other speed-control busbar C and thence through suchwattineter interlock contacts M as are closed to the raise-speedcontactors K of the running machines. Thus the speed of all machines(except those taking too great a load) is increased gradually andultimately the normal synchronous conditions are reestablished in amanner corresponding to that just described for the oppo site frequencychange, the interrupter relay J functioning as before at the appropriatemoment. 7

It will now be assumed that the load conditions have changed to-such anextent as to require an additional machine being brought into circuit.On this incoming machine the wattmeter interlock cont-acts M M are outof circuit owing to the fact that the circuitbreaker L is open and thetwo speed-control ccntactors K K are connected to the oppositespeed-control busbar-s C C through the synchronizing auxiliary contactsB B he circuit-breaker closing coil L is also connected throughsynchronizing auxiliary contacts B to the circuit-breaker closing busbarG and the synchronizing plug B is inserted to connect the leading phaseA of the potential transformer secondary to the synchroniz ing busbar CThis energizes the' changeover relay F whose contacts begin to lift, atonce deenergizing at contacts F the synchronizing relay E and ensuringthat its contacts are down before synchronizing operations commence. Thechange-over relay -F also breaks at F 5 the short-circuit across thetimelag relay H and substitutes at F the synchronizing busbar C for thelead to the A. G. generator D The synchronizing relays now, operate inaccordance with the phaserelationship between the voltages of theincoming and running machines.

Since the incoming machine speed is less than that of the runningmachines, (assuming that the machine was started up from rest), thesynchronizing relay E remains inoperative, and energizing current isintermittently supplied to one speed-control busbar G which is nowconnected to the raisespeed contactor K of the incoming machine. Thefurther "interruption in the supply of energizing current to theauxiliary motor K is brought about by the interrupter relay J as beforeat the appropriate moment, and these conditions continue untilsynchronous speed is reached and passed. The synchroscope needle nowcomes to rest and rotates in the reverse direction. During the firstrotation in the reverse direction the synchronizing relay E comes intooperation and at once energizes the time-lag relay H. Since the rate ofrotation of the synchroscope needle is at this stage very slow, thetime-lag relay contacts H complete their lift and complete theenergizing circuit through the circuit-breaker closing busbar C to thecircuit-breaker closing coil L of the incoming machine. After a timesufficient to allow the circuit-breaker L to close the interrupter relaycontacts J J short-circuit the time-lag relay H and break the circuit tothe speed-control busbars C O. The synchronizing plugs B B B B are nowremoved, with the result that the changeover relay F is deenergized toreestablish the normal frequency control circuits for comparison of thesystem frequency with the standard frequency, the load-sharing devices Malso operating to redistribute the load in view of the additionalmachine.

If it happens that the additional machine to be brought into circuit isalready rotating at a speed greater than synchronizing speed, whensynchronizing operations are commenced, the synchronizing relays willfunction in a manner generally similar to that described for frequencycontrol when the system frequency falls below the standard frequency,and the circuit-breaker closing circuit will be completed by theoperation of the time-lag relay contacts H when the lower-speedcontactor K has caused the auxiliary motor K to reduce the incomingmachine speed sufiiciently nearly to the synchronous value.

Figure 1 illustrates an adaptation of the above arrangement to theremote control from a control station of the frequency and loadconditions in a system supplied from a number of generating substations.The upper half of Figure 2 shows the control station equipment wherein anumber of control panels N N N one for each substation are provided,each control panel being connected through seven pilot wires O O O O O OO to its substation. One of the substation equipments is shown in thelower half of Figure 2.

The general principles governing this modification are that frequencycontrol of the whole system is carried out automatically from thecontrol station; automatic loadsharing between the individual machinestakes place in each substation; the distribution of load between thevarious substations i controlled by hand from the control station; andautomatic synchronizing of an additional machine is carried out in eachsubstation under the control of a selective remote control systemoperated from the control station. This selective remote control systemforms no part of the present invention and may be of any suitable kind,such that a selector device diagrammatically indicated at P P is causedby currents transmitted, say, over three pilot wires 0 O O to take upsuccessive positions in which contacts are operated respectivelyassociated with the individual machines in the substation. Only thoseparts of the remote control system are indicated which are of interestto the present invention, namely four selector contacts 1 P P P whichare closed when a particular machine has been selected to besynchronized and brought into circuit and correspond to the foursynchronizing plugs B B B B of Figure 1.

The remaining apparatus in the substation is to a large extent identicalwith that of Figure 1 and the corresponding parts are indicated forconvenience by small letters corresponding to the capital letters ofFigure 1, these parts not being described in detail except in so far asthey differ from Figure 1. Each machine a in the substation is providedwith a potential transformer whose secondary phase winding a is earthedwhilst the leading phase a is connected through the selector contact Pto a synchronizing busbar 0 The raise-speed and lower-speed contactors7a 1 4 are connected through auxiliary contacts Z Z on thecircuit-breaker Z either to speed-control busbars 0 c from thesubstation synchronizing apparatus or through the automatic load-sharinginterlock contacts m m to a pair of speed-control busbars Q 2alternatively energized from the local D. C. source 0 0 under thecontrol of a polarized relay Q connected across the pilot wires 0 O.

The synchronizing apparatus is identical with that of Figure 1 exceptthat the changeover relay F is omitted, the two sides of the resistance9 being connected to the two pilot wires 0 O which areenergizedrespectively from the lagging and leading phases R R 'busbars T Tleading to the frequency controlling apparatus. The pilot wires O aretaken respectively through contacts U U on a raise-load hand-switch Uand contacts V V ron a lower-load hand-switchv V and thence throughfrequency plugs S S to i speed-control busbars T T leading from thefrequency controlling apparatus. If the raise-load switch V is depressedthe pilots O O are directly connected to a local D. C. source T T?whilst if the lower-load switch is depressed the pilots O O areconnected to the same-D. C. source T T but with opposite polarity.

' The frequency controlling apparatus is generally similar to that ofFigure 1 and comprises a constant speed D. O. motor W driving an A. C.generator N one lead from which is earthed, whilst the other lead istaken to one side of an auxiliary synchronizing relay Y and to one sideof a resistance X the other side of which is connected to the leadingphase busbar T The other side of the auxiliary synchronizing relay Y isconnected to the midpoint of a resistance Y connected between theleading and lagging phase busbars T T A synchronizing relay X isconnected between the mid-point of the resistance X and earth throughthe normally open contacts Y of the auxiliary synchronizing relay Y, andmakes its own retaining circuit at X An interrupter relay Z is energizedfrom the local D. C. source T T under the control of normally closedcontacts Y on the auxiliary synchronizing relay Y, and is provided withnormally closed contacts Z Z respectively in series with normally closedcontacts Y Y on the auxiliary synchronizing relay and change-overcontacts X X on the synchronizing relay, these contacts controlling thepolarity of the current supplied from the D. C. source T T to thespeed-control busbars T T.

The operation of the frequency controlling apparatus, as also of thesynchronizing and load sharing apparatus in the substation will be clearfrom the description above given in connection with Figure 1.

Thus for controlling the frequency of a substation, the frequency plugsS S S S are inserted, and the frequency controlling apparatus willtransmit over the pilot wires 0 0 current of one polarity or the otherdepending on whether the frequency is'high or low. This will operate thepolarized relay Q which will act through the load-sharing contacts on mto energize one or other of the speed-control contactors Zck of thosemachineswhose speed is to be altered.

When it is desired'to raise the load taken by one substation, thecorresponding raiseload switch U is depressed. This first disconnectsthe pilots 0 0 from the frequency control apparatus and then connectsthem directly to the D. C. source T T whereby the polarized relay Q isoperated in such a direction as to raise the speed of all the machinesin the substation takingaverage or less than average load. An analogousoperation takes place on depression of the lower-load switch V. a i.

If the load conditions in the substation are such as to require theservices of an additional machine, the selective remote controlapparatus is operated to select the additional machine and to close thecontacts P P P P associated therewith. Thisbrings into operation thesubstation synchronizing apparatus which acts in the manner describedwith reference to Figure 1 to synchronize and bring into circuit theadditional machine.

It will be appreciated that the above arrangements have been describedby way of example only and may be modified in various ways within thescope of the invention.

hat I claim as myinvention and desire to secure by Letters Patent is 1.In electric synchronizing apparatus for maintaining constant thespeed'or frequency of an A. C. dynamoelectric machine, the com binationof a source of E. M. F. of standardfrequency, means for raising orlowering the speed of the machine, a relay device operative inaccordance with the relation between the machine speed and the standardfrequency, a source ofcontrolling current for energizing thespeed-controlling means, means whereby the relay device acts to controlthe transmission of impulses derived from such source for the selectiveoperation of the speed-controlling means, and means whereby the rate oftransmission of the impulses is gradually reduced as the machine speedisbrought into agreement with the standard frequency.

2. In electric synchronizing apparatus for controlling the frequency ofan electric system supplied from an A. G. dynamo-electric machine, thecombination with a source of E. M. F. of standard frequency, of a secondsource of E. M. F. derived from the system, a system of relays which areoperated in accordance with the relation between the frequencies of thetwo sources of E. M. F., a source of controlling current, means wherebythe relays act to control the transmission of impulses derived from suchsource for varying the speed of the machine, and means whereby the rateof transmission of the impulses is gradually reduced as the twofrequencies are brought into agreement. y

3. In electric synchronizing apparatus for controllingthe frequency ofan electric system supplied from a group of A. C. dynamoelectricmachines operating in parallel, the

" for controlling combination with a source of E. M. F. of standardfrequency, of a second source of E. M. E. derived from the system, arelay d vice responsive to the relation between the frequencies of thetwo sources of E. E, devices responsive to the load conditions in thesystem and acting to ensure a proper distribution of load to theindividual machines, and means whereby the relay device and theload-sharing devices act to control the frequency of the system.

4. In electric synchronizing apparatus for controlling the frequency ofan electric sy tem supplied from a group of A. C. dynamoelectricmachines opera ing in parallel, the combination with a source of E. M.F. of standard frequency, of a second source of E. M. F. derived fromthe system, a relay device normally resnonsive to the relation betweenthe frequencies of the two sources of E. M. E. and acting to control thefrequency of the system, and means whereby the same relay device can beutilized to control the synchronizing and bringing into circuit of anadditional machine.

5. In electric synchronizing apparatus for controlling the frequency ofan electric system supplied from a group of A. C. dynamoelectricmachines o erating in parallel, the combination with a source of E. M.F. of standard frequency, of a second source of E. M. F. derived fromthe system, a system of relays normally responsive to the relationbetween the frequencies of the two sources of E. M. E. and acting tocontrol the frequency of the system, a third source of E. M. F. derivedfrom the incoming machine, and a change-over relay which controls theconnection of the system of relays to the sources of E. M. F. wherebythe relays are responsive either to the first and second sources of E.M. E. or to the second and third sources of E. M. E, the same system ofrelays thus being utilized also for controlling the synchronizing andbringing into circuit of an additional machine.

6. In electric synchronizing apparatus for controlling from a controlstation the frequency of an electric system supplied from groups of A.C. dynamo-electric machines located in substations, the combination witha source of E. M. E. of standard frequency in the control station, of asource of E. M. E derived from the system in each substation andconnected to the control station through pilot wires, a system of relaysat the control station responsive to the relation between thefrequencies f the standard source of E. M. E. and any of the substationsources of E. M. E. to which they are connected, devices in eachsubstation for automatically controlling the dist 'ibution of loadamongst the individual machines in the substation, hand-operated meansat the control station the distribution of load amongst the substations,and means whereby the frequency-responsive relays or the handoperatedload-sharing means act in conjunction with the automatic load-sharingdevices to control the speed of the machines in each substation.

7. Electric synchronizing apparatus as claimed in claim 2, in which therelay device which is responsive to the relation between the frequenciesof two sources of E. M. F. comprises a plurality of relays including asynchronizing relay which receives its maximum energizing current whenthe two sources of E. M. F. are in phase with one another, and anauxiliary synchronizing relay which acts to render the synchronizingrelay inoperative when the frequency of the electric system is greaterthan that of the other source of E. M. F.

8. Electric synchronizing apparatus as claimed in claim 3, in which therelay device which is responsive to the relation between the frequenciesof two sources of E. M. F. comprises a plurahty of relays in cluding asynchronizing relay which receives its maximum energizing current whenthe two sources of E. M. F. are in phase with one another, and anauxiliary synchronizing relay which acts to render the synchronizingrelay inoperative when the frequency of the electric system is greaterthan that of the other source of E. M. F.

9. Electric synchronizing apparatus as claimed in claim 4, in which therelay device which is responsive to the relation between the frequenciesof two sources of E. M. F. comprises a plurality of relays including asynchronizing relay which receives its maximum energizing current whenthe two sources of E. M. E. are in phase with one another, and anauxiliary synchronizing relay which acts to render the synchronizingrelay inoperative when the frequency of the electric system is greaterthan that of the other source of E. M. F

10. Electric synchronizing apparatus as claimed in claim 5, in which thesystem of relays which is responsive to the relation between thefrequencies of two sources of E. M. F. includes a synchronizing relaywhich receives its maximum energizing current when the two sources of E.M. F. are in phase with one another, and an auxiliary synchronizingrelay which acts to render the synchronizing relay inoperative when theI frequency of the electric system is greater than that of the othersource of E. M. F.

11. Electric synchronizing apparatus as claimed in claim 6, in which thesystem of relays which is responsive to the relation between thefrequencies of two sources of E. M. F. includes a synchronizing relaywhich receives its maximum energizing current when the two sources of E.M. F. are in phase with one another, and

an auxiliary synchronizing relay which acts to render the synchronizingrelay inoperative when the frequency of the electric system is greaterthan that of the other source of E. M. F.

V 12. Electric synchronizing apparatus as claimed in claim 3, in whichwhen the share of the load taken by an individual machine lies outsidepredetermined limits, the loadsharing device associated with thatmachine acts to prevent the speed of the machine from being altered ifsuch alteration would tend to make the load taken by the machine deviatefurther from such limits.

13. Electric synchronizing apparatus as claimed inclaim 6, in which whenthe share of the load taken by an individual machine liesoutsidepredetermined limits, the load-sharing device associated withthat machine acts to prevent the speed of the machine from being alteredif such alteration would tend to make the load taken by the machinedeviate further from such limits.

14. In electric synchronizing apparatus as claimed in claim 6, thecombination with a system of relays in each substation for controllingthe synchronizing and bringing into circuit of an additional machine inthe substation, of a selective remote control arrangement for eachsubstation whereby an operator at the control station can select anindividual machine in the substation and cause the selected machine tobe synchronized and brought into circuit under the control of suchsystem of relays.

In testimony whereof I have signed my name to this specification.

THOMAS REGINALD WARREN.

